We plan to continue investigations of the effects of cannabis sativa and related cannabinoids on a set of behavioral and psychophysiologic measures in human subjects. The goal is to learn something about the actions of the drug and also to use the drug-induced changes to develop and refine neurophysiologic techniques useful for the study of normal perceptual processes as well as those seen in altered states of consciousness. Particular attention will be paid to the determinants of subjective alterations and the relationship between subjective state and objective measures. Evidence for tolerance and dependence using improved neuropsychological techniques will be sought. The methods include electroencephalographic evoked potential techniques sensitive to complex psychological function, performance on information processing tasks and the systematic measurement of physiologic and subjective reactions to the drugs. Comparisons of similarities and differences of cannabis and other drugs (alcohol, cannabinoids and lysergic acid diethylamide) when given to subjects experienced in the use of such drugs will be part of the study.